GH4169合金δ相的溶解行为及对变形机制的影响

采用光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)技术和透射电镜(TEM)研究GH4169合金中δ相在高温变形条件下的演变规律,分析δ相的溶解过程及其动力学机制,探讨δ相对GH4169合金高温变形动态再结晶机制的影响。结果表明:随变形温度的升高或应变速率的降低δ相含量减少,动态再结晶晶粒尺雨和体积含量增大,δ相主要以弯曲、扭折和切断等方式来协调塑性变形,并在界面能降低的驱动力下由针状逐渐转变为短针状乃至球状;在高温变形条件下,δ相的溶解时间大大缩短,位错、空位和曲率对δ相的溶解起到重要作用,这主要与其对溶质原子扩散行为的影响有关,变形过程中产生的大量高密度位借及空位为溶质原子提供了众多高速率扩散通道,促进了δ相的溶解;δ相的存在改变了GH4169合金的动态再结晶机制,其动态再结晶机制主要有δ相诱发动态再结晶形核和非连续动态再结晶形核。     

固体中一种新发现的扩散机制—复合体扩散机制SCIEI

置换溶质原子可以以溶质原子-空位复合体形式扩散,这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律,密排晶体中溶质原子的异常快速扩散现象,B在γ-Fe中快速扩散和晶界非平衡偏聚,溶质原子在Al表面空位坑中的聚集以及Si在Al晶界处析出等问题。     

GH4720Li合金双道次热压缩变形过程的组织演变

对GH4720Li合金在1080~1180℃、应变速率为0.1s~(-1)条件下的双道次压缩过程的热变形行为进行研究。结果表明:动态再结晶是GH4720Li合金的主要软化机制。在双道次压缩间歇期内,合金发生亚动态再结晶、静态再结晶和晶粒长大;低于1120℃的变形间歇期,亚动态再结晶、静态再结晶和晶粒长大的速度缓慢;1120℃及以上温度的变形间歇期,亚动态再结晶、静态再结晶和晶粒长大的速度加快。随变形温度升高和第一道次变形量增大,道次间歇期的亚动态再结晶和静态再结晶速度加快。γ′相在热变形过程中发生协调变形,并发生细化。     

固体中一种新发现的扩散机制──复合体扩散机制SCIEI

置换溶质原产可以以溶质原子－空位复合体形式扩散，这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律，密排晶体中溶质原子的异常快速扩散现象，Ｂ在γ－Ｆｅ中快速扩散和晶界非平衡偏聚，溶质原子在Ａｌ表面空位坑中的聚集以及Ｓｉ在Ａｌ晶界处析出等问题．     

A NEWLY DISCOVERED DIFFUSION MECHANISM IN SOLIDS──COMPLEX DIFFUSION MECHANISM

置换溶质原产可以以溶质原子－空位复合体形式扩散，这一扩散机制可以圆满的说明非平衡偏聚现象发生的规律，密排晶体中溶质原子的异常快速扩散现象，Ｂ在γ－Ｆｅ中快速扩散和晶界非平衡偏聚，溶质原子在Ａｌ表面空位坑中的聚集以及Ｓｉ在Ａｌ晶界处析出等问题．     

定向凝固Al-4%Cu合金微观组织和溶质浓度影响因素研究

以Al-4%Cu亚共晶合金为研究对象,研究不同试样尺寸、初始变形量以及晶体取向条件下定向凝固单晶Al-4%Cu合金微观组织、固溶体中溶质浓度变化,以及凝固过程中溶质的分布规律和影响因素。结果表明,随着试样直径增大,Al-4%Cu合金内非平衡共晶相体积分数提高,Cu溶质成分曲线越平缓,α-Al固溶体Cu溶质分布更加均匀,晶内偏析减小,这主要是由于大尺寸试样熔体中自然对流更加充分,促进了溶质在液相中的扩散,减轻了固液界面前沿溶质的富集;施加一定塑性变形后,由于变形导致试样中位错密度增加,位错增殖和运动过程中形成的空位缺陷可以容纳更多溶质原子,因而凝固初期Cu成分曲线升高,α-Al固溶体中溶质浓度增大;对于不同取向的试样,随着晶体取向偏离[001]方向角度增大,微观偏析先降低后增大,而固溶体中溶质浓度先增大后降低。这是由于固/液界面能存在各项异性,溶质原子进入固/液界面的难易程度与晶体取向相关,不同晶面原子的吸附能力不一致,从而导致固液界面前沿溶质富集和固溶体中溶质浓度存在差异。     

Cu-Ni-Si合金二次时效时的再结晶行为

利用透射电镜、显微硬度法和电导率法,研究了Cu-Ni-Si二次时效过程中显微组织、硬度及导电率变化情况.结果表明:二次时效可使合金在较短的时效时间内获得更高的导电率,经预时效后冷变形的合金,溶质原子可借助密集且分布均匀的位错网络由铜基体快速传输至析出物处或析出物的形核部位完成析出过程,使铜基体得到快速的净化,从而获得较高的导电性.Cu-3.2Ni-0.75Si合金经预时效 变形后的时效过程中,可发生原位再结晶和不连续再结晶两种形式的再结晶.再结晶的形式主要决定于预时效时析出相的大小和冷变形的程度,稳定细小的析出相促使原位再结晶的发生,原位再结晶使合金微观组织中析出相比较细小,因而保持较高的硬度;亚稳的析出相在再结晶过程中将向稳定相转变,相变动力与形变储存能共同作用促使合金发生不连续再结晶,使合金硬度迅速下降,析出相快速粗化.     

外场处理在镍基高温合金组织控制中的应用

在镍基高温合金的热处理中施加静电场或脉冲电流,研究外场作用下合金组织结构的演化行为及机制。结果表明,静电场处理（EFT）可以促进合金中的空位运动,使合金中孪晶界面比例显著增加;静电场可以促进原子扩散,改变合金中沉淀相形核、长大的热力学及动力学条件。在镍基高温合金的塑性变形过程中进行脉冲电流处理（EPT）,可显著降低合金的塑性变形抗力、提高其塑性变形能力。同时,脉冲电流可以降低合金的再结晶激活能,促进再结晶晶核的形成及长大。     

Al-Zn对称成分合金不连续析出组织的再结晶

采用光学显微镜、扫描电镜和透射电镜研究了Al 4 0 %Zn(摩尔分数 )二元合金的不连续析出细片层组织在冷轧后重新加热时所发生的再结晶。根据加热过程中的显微组织变化 ,确定了该合金再结晶的形核及长大机制。结果发现 ,再结晶的 2种机制为非典型形核长大机制的连续粗化和典型形核长大机制的不连续粗化 ,后者又分为在团域界面、滑移带等处发生的以变形储能为主要驱动力的粗化和在变形量很小区域发生的以界面能为主要驱动力的粗化。     

HCP晶体中溶质原子异常快速扩散现象的机制

根据本文提出的转换溶质原子－空位复合体扩散的机制，估算了ＨＣＰ晶体中某些具有异常快速扩散现象的溶质原子的扩散系数，结果表明复合体扩散机制可以很好地解释此现象。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。